This invention relates to a resist material used for production of semiconductor devices, etc. Particularly, the present invention relates to a resist material for forming a positive pattern using deep ultraviolet (DUV) light having a wavelength of 300 nm or less, such as KrF excimer laser beams having a wavelength of 248.4 nm, etc.
In recent years, the wavelength of light from the light source of an exposing apparatus used for micro-fabrication, in particular, photolithography has been shortened with an enhancement of the packing density of semiconductor devices. Now, employment of KrF excimer laser beams (248.4 nm) has come to be investigated. However, a resist material suitable for this wavelength has not yet been found.
For example, as resist materials used in the case of using a light source capable of oscillating KrF excimer laser beams or deep ultraviolet light, there have been developed dissolution-inhibiting type resist materials comprising a resin having high transmittance for light of 248.4 nm and a photosensitive compound having a diazodiketo group in the molecule (for example, Japanese Patent Unexamined Publication Nos. 1-80944, 1-54048, 1-155338, 1-155339 and 1-188852, and Y. Tani et al., SPIE's 1989 Sympo., 1086-03, etc.). However, these dissolution-inhibiting type resist materials, in common with one another, have a low sensitivity and hence cannot be used in the case of employment of deep ultraviolet light or KrF excimer laser beams which requires a highly sensitive resist material. On the other hand, for reduction of the exposure energy (enhancement of the sensitivity), there has been proposed recently a chemical amplified type resist material in which an acid generated by exposure to light is used as a catalyst [H. Ito et al., Polym. Eng. Sci., 23, 1012 (1983)]. On such chemical amplified type resist materials, various reports have been presented [for example, H. Ito et al., U.S. Pat. No. 4,491,628 (1985); J. V. Crivello, U.S. Pat. No. 4,603,101 (1986); W. R. Brunsvolt et al., SPIE's 1989 Sympo., 1086-40; T. Neeman et al., SPIE's 1989 Sympo., 1086-01; and Japanese Patent Unexamined Publication No. 62-115440 (U.S. Pat. No. 4,603,101)]. Such chemical amplified type resist materials, however, involve the following problems. When there is used in them a phenol ether type resin such as poly(4-tert-butoxycarbonyloxystyrene), poly(4-tert-butoxycarbonyloxy-.alpha.-methylstyrene), poly(4-tert-butoxystyrene), poly(4-tert-butoxy-.alpha.-methylstyrene) or the like, all of the chemical amplified type resist materials have poor thermal stability and are disadvantageous in that because of their low adhesive properties to a substrate, film peeling tends to occur during development, so that no satisfactory pattern can be obtained. When there is used a carboxylic acid ester type resin such as poly(tert-butyl 4-vinylbenzoate) or the like, the chemical amplified type resist materials are insufficient in light-transmitting properties near 248.4 nm because of the aromatic ring. When there is used a poly(tert-butyl methacrylate) or the like, the thermal stability and dry etching durability of this resin are poor. As resist materials free from the above defects, there have recently been reported a resist material obtained by use of a copolymer of p-tert-butoxycarbonyloxystyrene and p-hydroxystyrene (Japanese Patent Unexamined Publication No. 2-209977 (EP 366,590)), a resist material obtained by use of a copolymer of p-tetrahydropyranyloxystyrene and p-hydroxystyrene (Japanese Patent Unexamined Publication No. 2-19847 (U.S. Pat. No. 5,069,997, U.S. Pat. No. 5,118,585)), a resist material obtained by use of a copolymer of p-tert-butoxystyrene and p-hydroxystyrene (Japanese Patent Unexamined Publication No. 2-62544), etc. However, when a pattern formation is carried out using such a resist material, there takes place a loss of critical dimension of pattern with a time delay between exposure and post-exposure bake (hereinafter referred to as "PEB"). Therefore, even if a pattern can be formed in a remarkably short time, a good pattern formation cannot be expected in a practical production wherein a considerable time is required from the light exposure to PEB. Thus, such resist materials are disadvantageous in that they are of little practical use. Further, the resist materials obtained by use of the above-mentioned polymers or copolymers are, in common with one another, disadvantageous in that the difference in dissolution rate for an alkali developer between light exposed areas and non-exposed areas of the resist material is small, resulting in making resolution ability insufficient.
In addition, acids generated by photosensitive compounds capable of generating an acid upon exposure to light (hereinafter abbreviated as "photoacid generators") which are used in conventional chemical amplified type resist materials, are strong acids such as Lewis acids and sulfonic acids. Therefore, the acids are neutralized even in an atmosphere containing a slight amount of a basic substance such as organic amines or ammonia which are generated in the production of a semiconductor device, so that chemical amplification is not sufficiently caused, resulting in, for example, the following problem: the dimensions of a pattern are changed, or no good profile of pattern can be obtained.
Thus, although the chemical amplified type resist materials have a higher sensitivity than do conventional resist materials, they involve problems of, for example, poor in thermal stability of resin, poor in adhesion strength to a substrate, insufficient in transmittance for light of near 248.4 nm, insufficient resolution, and the impossibility of attainment of a good profile of pattern, and change of the dimensions of a pattern with the lapse of time which are due to insufficient chemical amplification. Therefore, they are difficult to put to practical use. Accordingly, there is eagerly desired a practical highly sensitive resist material free from all of the above problems.